Dear Duong Le Duy Thai

First of all, there is no dumb question if you want to know something you currently do not.

Secondly, the chromosome is not translated entirely when needed; only the functional units (genes), that are located at a specific locus on a specific chromosome, are transcribed and then translated into proteins to function in a specific way.

Since we have 2 copies from each chromosome, each is derived from one parent, so we have 2 copies from each gene (we have 2 alleles for each gene).

When the body requires a specific protein to perform a specific function, the two copies of the gene responsible for coding for this protein would be transcribed inside the nucleus and then translated in the cytoplasm (in the rough endoplasmic reticulum) to make a protein that has the required function.

If one copy of a gene (e.g. that was derived from the father or sperm) is mutated (i.e. abnormal), there will be production of an abnormal protein along with the normal protein (from the other normal gene copy).

This would lead to appearance of signs and symptoms of a disease if the disease / trait is dominant but would not manifest if it was a recessive one (i.e. the individual who carries one mutant plus one normal allele for a recessive disease is called a carrier).

Hope this brief is helpful.

Regards

Dear Mr. Bassam MS Al-Musawi

Thank you so much for your answer. But can I ask another question:

As your answer, both of the parent genes are transcribed, but I wonder how can a gene is dominant? I mean they are both transcribed so the number of protein translated should be equal right?

A gene cannot be said to be (dominant) or (recessive) but the traits / diseases can. What determines this is the need of the body to that protein.

You know that each allele codes for 50% of the protein and both alleles contribute to 100% of the produced protein.

Different proteins are required by the body to maintain normal function in different amounts. Some are high but others are lower.

If the body always require high amounts (e.g. >90%) of a particular protein to maintain its normal function, then a mutation in one allele would lead to loss of the normal protein which would be produced by 50-60% only [as the mutation in the other allele does not necessarily lead to loss of protein function entirely]. The end result is that we would have only 50-60% of the protein that is NOT enough to maintain normal function by the body so a disease state occurs due to protein deficiency (e.g. structural proteins, hormones, key enzymes, membrane receptor, etc.).

This occurs in dominant types of diseases, the protein is required in high quantities all the time.

While if the amount of protein required by the body to maintain normal function was around 50%, then mutation in one allele leads to loss of 50% of this protein and the remaining 50% would be enough to maintain normal function. It exceeds the margin of safety of the body's needs, so nothing abnormal occurs despite the individual having a mutant allele.

An affected individual would have 50% risk of having an affected baby in each pregnancy.

This is called a carrier state for recessive gene disorders. Here the disease manifestations mostly occur when both alleles are mutant (i.e. both parents carry one abnormal allele), there will be 25% risk of having an affected baby in each pregnancy.

Hope this explanation was helpful.

Regards

Dear Mr. Bassam MS Al-Musawi

Thank you again for your answer. I appreciate your help extremely.

Best regards

Dear Duong Le Duy Thai,

Let me make short comment. As Mr. Al-Musawi said - "A gene cannot be said to be (dominant) or (recessive)..." and it is very important. In a population, a gene can be represented by one, two, ten, or more alleles. It is more correct to speak dominant or recessive alleles. But their dominance-recessivity is determined by how products of certain gene alleles perform their functions in the body. If the mutant allele leads to the loss of its product (RNA or protein) and, consequently, its function, and the second (normal) allele is enough to fulfill this function, the “normal” allele will be called dominant, and the mutant will be called recessive. In the case of a reverse situation (the inability of 50% of the product to fulfill its function in the body), the mutant allele will be called dominant, and the normal allele will be called the recessive one, etc. as described already by Mr. Al-Musawi. As some genes are consist of many alleles, some of them (alleles) can be dominant to ones, and at the same time recessive to other alleles.

Hope, my comment will be helpful,

Best wishes